Blue print coating



portant single use for blue print paper.

Patented July 4, 1939 PATENT f OFFICE BLUE PRINT COATING Garnet Philip Ham,

signor to American York, N. Y.,

Old Greenwich, 001111., as-

Cyanamid Company, New .acorporation of Maine [1N0 Drawing: Application July 16, 1938,

* Serial No. 219,599

6 Claims.

This invention'relates to blue print coatings and more particularly to blue print coatings having improved printing characteristics with respect to speed and latitude.

Blue print coatings in general consist of a light sensitive ferric salt, a ferricyanide, and other substances which may be necessary to pro-' duce the desired solution pH. In general in the past, potassium ferricyanide has been standard as the ferricyanide component of blue print coatings, and ferric ammonium oxalate has been used where fast printing coatings have been desired, other ferric salts such as the citrate being used where slower speed is unobjectionable.

According to the present invention, certain sensitizers are added to the blue print coating which increase the printing speed of the coating and do so without any sacrifice in latitude but with an actual increase in latitude vso that in spite of very greatly increased printing speeds,

practically pure white backgrounds can be readily obtained which is an important factor in the reproduction of line drawings, the most im- These sensitizers are compounds of strong organic bases included in the group consisting of amidines and quaternary ammonium compounds. While the invention is not broadly limited tothese groups, I have found that the compounds which are rather strongly basic, such as the quaternary ammonium hydroxides and the carbonates of the amidines, give results which are superior to those obtained with compounds of the organic bases with relatively strong acids. Among the'many compounds included in theinvention, two have proven to be of particular effectiveness, namely, guanidine carbonate and trimethylbenzylammonium hydroxide (obtainable in the trade'under the name Tetrone B).

I have found that the eflectiveness of the sensitizers of the present invention varies to aconsiderable extent with the relative amount of sensitizer and ferricyanide or ferriand ferrocyanide in the coating. The improved effect does not continue to increase with increased amounts of sensitizers but passes through a maximum, thereafter declining so that "both very small amounts of sensitizer'and very large amounts of sensitizer give results which are relatively poor as compared to those obtainable within the op timum range. This 'range is not highly critical.

Good results are obtained with an amount of the sensitizer stoichiometrically corresponding to the total ferriand ferrocyanide present. Results are improved with the addition of larger binations where amounts of sensitizer, and a maximum is reached in most cases when the amount of sensitizer is stoichiometrically equivalent to twice the total ferriand ferrocyanide present in the coating. Additional amounts of sensitizer result in a lowering of activity and therefore, while the invention in its broader aspects is not limited to a particular proportion of sensitizer, in more specific aspect a proportion of sensitizer approximately twice the stoichiometrical equivalent of ferriand ferrocyanide content is included as a specific preferred modification of the invention.

I have not as yet been able to determine the mechanism by which the sensitizers operate, and the present invention is not intended to be limited to any theory of action. I do believe, however, that there .is some chemical relationship between the sensitizer and the iron-cyanogen complex, and this is advanced as a probable explanation of the operation of the present invention without in any way limiting it thereto. It is an advantage of the present invention that the addition of sensitizers increases both speed and latitude of blue print coatings containing either potassium ferricyanide alone, mixtures of potassiumferriandferro-cyanide, sodium ferricyanide alone, or mixtures of sodium ferricyanide and sodium ferrocyanide. I have found that results are, however, obtained when the best'ot the sen'sitizers of the present invention, that is to say, such strongly basic sensitizers as'guanidine carbonate and the. quaternary ammonium hydroxides, are used with a sodium ferricyanide liquor to which additional sodium ferrocyanide has been added. The increase in latitude is particularly eflective in conjunction with such comotherwise the printing speed sometimes results in slightly 'I have not as yet been able'todetermine the reason for the extraordinary'latitude combined with high-speed which is obtained with the best of the sensitizers of t e present invention. is an unusual result since normally factors which increase printing speed decrease 'latitudeand cause trouble with backgrounds and, while I have anation for this ex- K at present no 'proven exp traordinary behaviour of the sensitizers of the v present inventiomit constitutes one of their most important advantages since all of the desirable results of high speed out any compromise on The invention will be v tail in conjunction with examples which illustrate typical embodiments background quality. J

described in greater deof the present invention which, however, -is not optimum colored background.

printing are obtained wlth-' the following specific 2 limited to the details therein set forth and par-. ticularly is not limited to the illustrative compounds of the strong organic bases therein described.

Solution B is added to Solution A at a temperature of approximately 35 to 40 C., the addition being in the absenceof actinic light and with sufhcient agitation to ensure thoroughmixture. 3.5! parts of 90% pure guanidine carbonate are then added and the entire solution cooled to 25 C., whereupon 0.5 part citric acid is introduced. The final solution has a pH of approximately 7.7 andmay be used for coating paper at room temperature or slightly elevated temperatures, all steps, of course, being in the absence of actinic light. The paper was compared with a premium paper of high speed printing'characteristics using conditions of machine printing corresponding to the CF Pease #20 continuous blue printing machine. The blue intensity at 6 secs. exposure 15 feet per minute) was almost of the same depth as on the premium paper at 42 secs. exposure (2 feet per minute). Normal pfast running is 10 feet per minute. Pure white backgrounds were obtained, and the coating showed high quality for the reproduction of line drawings and was also suitable for contact printing from negatives giving pictures of good detail. At the highest machine speeds at which the above machine can run (about 19 feet per minute), the blues were still of satisfactory depth for good-reproduction.

of line drawings and were notably deeper than the premium grade commercial paper at the same speed.

v Exlunu 2 Two solutions were prepared as follows:

Solution A 7 Parts Water 50 Potassium oxalate 2. 5 Ferric ammonium oxalate 20 Solution B V Parts Water 3'? Sodium ferricyanide liquor 13 Sodium fefiocyanide 2.83

In Solution B the normal ferricyanide liquor which contains approximately 1.33% sodium ferrocyanide has been enriched" with additional sodiumferrocyanide. Solution B is' added to I Solution A as described in'Example 1, then 3.57, parts of 90% guanidine carbonate introduced, the

solution cooled and 1 part of citric acid added to give a pH of approximately 6.85. The solution is then ready for coating paper at room temperature or slightly elevated temperatures. All operations are, of course, carried out in the absence:

'- of'actini light. 76

7 The p per shows an even higher speed than that of Example 1, and the latitude is slightly greater. Even at the very slowest printing speeds,

EXAMPLE 3 "Thespeed of the paper coated according to.

Example 2 was so high that with tracings of high translucency, even at the highest useful printing speeds, the paper was faster than necessary. Therefore, a paper was made similar to Example 2 but with slightly less speed. This was eifected by reducing the amount of sodium ferrocyanide in Solution B from 2.85 parts to 1.5 parts and cutting the amount of citric acid in half. The resulting pH was about 7.35, and a paper was obtained having a speed somewhat less than tha of- Example 1 but still better than premium paper available on the market.

ExAMPLn 4 A solution was made up as in Example 3 but 0.04 part of water-soluble nigrosine was added.

The resultingsolution was coated onto paper and gave a stronger blue approaching in strength that of Example 1. The nigrosine washed off the paper V completely, leaving no stain in the background,

but apparently exerted some effect on the depth of the blue shade.

EXAMPLE 5 A blue print coating was prepared in accordance with Example 1 except that, in the place of 3.57 parts of guanidine carbonate, 11 parts of trimethylbenzylammonium hydroxide were used, the pH solution being '7.6. The paper produced showed approximately the same character"- istics as that of Example 1.

Solution B is added to Solution A as described. in Example1 and then 1.2 parts of guanidine nitrate were added, followed by 1 part of, citric acid. Paper was coated and showed a printing speed approximatingthat of Example 3.

It will be noted that guanidine nitrate is not as effective a sensitizer as guanidine carbonate.

EXAMPLE 7 A coating solution is prepared according to Example 1, but instead of guanidine carbonate, 1 part of guanyl-urea sulfate is substituted. A fast printing paper is obtained, but the latitude is not as satisfactory as with guanidine carbonate, white backgrounds being unobtainable with very long printing speeds.

Doubling the amount of guanyl-urea sulfate and citric acid produced a pure white background but reduced the printing spe'ed down to approximately that of. premium commercial paper.

What I claim is: l. A blue print coating composition comprising a light sensitive ferric salt, a soluble ferricyanide and an amidine salt in an effective amount.

2. A blue print coating composition comprising a light sensitive ferric salt, a soluble ferricyanide and a strongly basic amidine salt in an eflective amount.

3. A blue print coating composition comprlsing a light sensitive ferric salt, a soluble ferricyanide and a guanldine compound in an effeci tive amount.

4. A plue print coating composition comprising a light sensitive" ferric salt, a soluble ferncyanide and guanidine carbonate in an effective amount.

5. A blue print coating composition according metrically equivalent to approximately twice the ferricyanide.

6. A blue print composition according to claim 4 in which the amount of guanidine carbonate is stoichiometrically equivalent to approximately twicethe ferricyanide.

GARNET PHILIP to claim 1 in which the amidine salt is stoichio- 

